Well-Defined Macromolecule-Magnetic Nanoparticle Complexes

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Intellectual Merit of the Research Program. This research focuses on the molecular design of block copolymers with anchor segments expected to bind to magnetic metal or metal oxide particles and tail blocks to provide steric dispersibility in aqueous and organic carrier media. Emphasis is devoted to two inter-related thrusts. One includes syntheses of copolymer dispersants with hydrophobic, glassy anchor blocks and controlled molecular weight tails, a study of their function as micellar templates for generating controlled-size cobalt nanoparticles, dispersive properties as related to particle size and copolymer structure/morphology, and anaylses of their effectiveness in improving durability of magnetic metal nanoparticles. The second thrust encompasses the design of enzymatically degradable dispersants for magnetite, and a study of dispersibility as related to magnetic size as it is increased from 10-100 nm in diameter. These dispersants have silane or siloxane anchors with carboxylate binding groups and selected peptide tail blocks. The polypeptide blocks include models with essentially uni-modal molecular weight distributions as compared to those prepared in facile polymerizations via carbodiimide-activated aminoacid coupling or by ring-opening of N-carboxyanhydrides. Anticipated outcomes of teh research are methodologies for preparing controlled size cobalt and magnetic nanoparticles, well-coated with macromolecular dispersants. The knowledge gained relating copolymer structure and composition, particle size, and dispersibility will enable complexes to be prepared with the highest possible volume fractions of the magnetic components. This will provide dispersible magnetic complexes with the highetst magnetic response. It will also provide a firm basis for predicting properties of other particle-macromolecular compositions as future inorganic magnetic components are developed. Anticipated Broader Aspects of the Program: Complexes of tailored macromolecules with magnetic metal and metal oxide nanoparticles could "open the door" to microelectronics and critical biomedical technologies. Biological applicatons include possibilities for intra-arterial, magnetic field-directed localization of drugs, cell targeting with magnetic separations for bone marrow treatments, localized in-vivo hyperthermia treatments for treating difficult-to-reach malignancies with heat generated via alternating magnetic fields, improved diagnostic imaging tools, and treatments for retinal detachments. The development and understanding of tailored macromolecular dispersants hold the key to obtaining materials with the maximum volume fraction of the magnetic component in the complexes that remain dispersible in the necessary carrier media. It is also probable (1) that the solution structures of the reaction media for synthesizing these nanoparticles can be used to control the in-situ generated particle size, (2) that improved polymer coatings can impart biocompatibility, and (3) that these coatings can improve particle durability against oxidation. The program will concentrate on educating graduate students. In this vein, it is recognized that today's fundamental research methods are multi-disciplinary and global. The students will enhance needed team-building and communication skills by collaborating throughout the program on inter-related research thrusts, by completing a 1-cr. course each in technical writing and in technical oral communication, and by annual participation in scientific meetings to present research findings. They will participate in an international multi-disciplinary working group by electronically sharing ideas, and by preparing model materials for study for physicists and pharmacologists in the group. In this way, they will derive multi-disciplinary research findings related to their materials and will also contribute to a research infrastructure whereby the physicists and pharmacologists will be able to conduct careful studies on well-defined macromolecules and macromolecular-magnetic particle complexes.